CHARLOTTE, N.C. — San Antonio Mayor Julián Castro and first lady Michelle Obama made emotional prime-time pitches Tuesday to two crucial constituencies — Hispanic voters and women — appealing to the importance of family and warning that losing the White House could turn back the gains of a generation.

Castro, a 37-year-old grandson of immigrants and rising star in the Democratic Party, mixed a robust defense of President Barack Obama’s record with his family’s story, which he said is an American story.

“Ours is a nation like no other — a place where great journeys can be made in a single generation,” he told thousands of delegates to their national convention. “No matter who you are or where you come from, the path is always forward.”

That invoked the Obama campaign slogan and a key theme for the opening night of the three-day Democratic gathering in a swing state that Obama surprisingly captured in 2008. Democrats aimed to make their case for the president’s re-election by drawing a sharp contrast with Republican nominee Mitt Romney, who used his convention last week to blame Obama for the nation’s economic woes.

Much as Ann Romney did last week in Tampa, Fla., for the GOP nominee, the first lady took the national spotlight Tuesday to deliver a family-friendly tribute to Obama as husband and father.

“Barack knows the American dream because he’s lived it,” she said. “And he believes that when you’ve worked hard, and done well, and walked through that doorway of opportunity, you do not slam it shut behind you. You reach back and you give other folks the same chances that helped you succeed.”

Castro used his family narrative to amplify the party’s message of opportunity and investment.

“Texas may be the one place where people actually still have bootstraps … and we expect folks to pull themselves up by them,” he said. “But we also recognize there are some things we can’t do alone. We have to come together and invest in opportunity today for prosperity tomorrow.”

Castro is little-known outside Texas, but Tuesday’s high-profile address offered an opportunity to lift his political profile. His selection as a convention keynote speaker underscored the importance of a growing Hispanic population that is key to Obama’s re-election efforts in swing states including Colorado, Florida and Nevada.

The address came 24 years after another little-known Texan, Ann Richards, delivered the keynote that launched her political career.

Castro was introduced by his identical twin, state Rep. Joaquín Castro, who is running for Congress. They shared a hug and Julián Castro held his brother on stage for a moment to wave to the crowd, the pair distinguishable only by the color of their suits and ties (Julián’s blue, Joaquin’s purple) and the wedding ring worn by Julián, the older twin by just a minute.

New generation

They are part of a new generation of Texas Democrats leaders hope will lead a resurgence to two-party status in a state where Republicans hold every statewide office.

The Castro brothers were raised by a single mother who became a leader of the La Raza Unida civil rights movement that promoted Chicano rights. When Julián Castro mentioned her, the crowd chanted her name, “Rosie,” as she looked on.

It reflected the gusto with which he delivered his speech, sparking waves of applause.

He also recalled his late grandmother, Victoria, an orphan who emigrated from Mexico in 1920.

“My grandmother didn’t live to see us begin our lives in public service,” Castro told the convention. “But she probably would’ve thought it extraordinary that just two generations after she arrived in San Antonio, one grandson would be the mayor and the other would be on his way — the good people of San Antonio willing — to the United States Congress.”

In a vigorous critique of the Republican ticket, Castro said the Romney-Paul Ryan agenda on taxes, health care, job training and public education “doesn’t just pummel the middle class — it dismantles it.”

“Of all the fictions we heard last week in Tampa, the one I find most troubling is this: If we all just go our own way, our nation will be stronger for it. Because if we sever the threads that connect us, the only people who will go far are those who are already ahead,” he said.

Republicans say the Obama administration’s economic record has hurt Latinos, and they noted the promises of Obama’s own Democratic keynote address, eight years ago, contrasted with the division in the country during his presidency.

“The 2.3 million Hispanics that now find themselves in poverty, they know the numbers well — the high cost not only of education but of health care and gasoline,” said Jovita Carranza, former deputy administrator for the U.S. Small Business Administration under President George W. Bush.

Castro also poked fun at Romney by casting him as the out-of-touch scion of family wealth. He noted that during a campaign stop at a university in Ohio, Romney gave students entrepreneurial advice about how to start a business: “Borrow money if you have to from your parents.”

“Gee, why didn’t I think of that?” Castro said. “Some people are lucky enough to borrow money from their parents, but that shouldn’t determine whether you can pursue your dreams. I don’t think Governor Romney meant any harm. I think he’s a good guy. He just has no idea how good he’s had it.”

Castro’s reflections

Earlier Tuesday, over lunch at a hotel near the convention center, Castro discussed Texas politics, the legacy of Richards and how as mayor of San Antonio he has attracted support from blue-chip business interests in support of a sales tax increase to expand pre-kindergarten education. It’ll be on the ballot in the city this fall.

“There’s no way to sugarcoat it — tax has three letters, but it’s a four-letter word. I don’t care about that,” he said.

A Democrat has not been elected to statewide office in Texas since 1994. Castro said he’s confident that Democrats will begin winning statewide offices again.

“The question is, how many years?” he said. “It’s going to be sooner rather than later.”

He said Hispanics need to vote in numbers that better reflect their percentage of the population. And he predicted that Democrats will benefit from the influx of people from other states.

“That infusion of people from more moderate states is going to change the political landscape,” he said. “I do believe the state is going to turn purple, then blue. And Democrats do have a substantial farm team. The question for everybody is, when do you run?”

Keeping score

Rating the Democrats’ convention strategy:

On track: Facing a tough judgment from voters on the question, “Are you better off than four years ago?,” Democrats put the best possible face on President Barack Obama’s first term. They reminded voters of the deep financial crisis of 2008, hailed the bailout of the auto industry, and noted that the economy is adding jobs — even if slowly — rather than losing them. And they passionately defended his signature health care law, even in the face of its unpopularity.

Off balance: The party risks overplaying its hand on the killing of Osama bin Laden. Speaker after speaker turned military victory into a partisan talking point, the very kind of politicization they decried during the Bush administration. Touting the president’s leadership and decision-making without seeming to gloat is a careful line to toe.